Multi-level optical recording medium, multi-level recording method, and multi-level reproduction method

ABSTRACT

A multi-level optical recording medium according to the present invention is a multi-level optical recording medium ( 1 ) which is capable of recording record data according to multi-level recording that defines light reflection ratios of recording portions ( 12 ) into multiple levels by switching the irradiation amount of a recording laser beam between multiple levels, wherein light reflection ratio information enabling identification of a light reflection ratio dynamic range within which respective light reflection ratios of the recording portions ( 12 ) should be included is readably recorded. Due to this construction, when record data are recorded, it is only required to record the record data such that the respective light reflection ratios of the recording portions ( 12 ) are included within the light reflection ratio dynamic range identified from the light reflection ratio information, and it is unnecessary to perform the operation of checking the characteristics of the multi-level optical recording medium ( 1 ) prior to recording the record data. Therefore, it is possible to record the record data promptly and easily without wastefully using a data-recording area.

TECHNICAL FIELD

This invention relates to a multi-level optical recording medium capableof carrying out multi-level recording on one virtual recording cell, anda multi-level recording method and a multi-level production method forthe multi-level optical recording medium.

BACKGROUND ART

At present, as an optical recording medium, there is widely used abinary optical recording medium which is configured to record binarydata by a pit formed by irradiation of a recording laser beam and enablethe binary data to be reproduced based on whether the pit is present orabsent. Further, in recent years, to meet the requirement of enhancingrecording density of optical recording media, research has beenconducted into the recording of data in high density by adjusting thefocused beam diameter of a recording laser beam. On the other hand, amulti-level optical recording medium is being developed which is capableof recording one of different marks having a plurality of meanings,respectively, on one virtual recording cell, differently from the methodof adjusting the focused beam diameter. In the multi-level opticalrecording medium, there are utilized, for example, characteristicsthereof in which by switching the irradiation amount of a recordinglaser beam between multiple levels, a portion changed in properties(hereinafter referred to as a “recording mark”) appears in a portion ofone virtual recording cell as a recording object in the opticalrecording medium, causing reduction of the light transmission ratio ofthe cell, and at the same time a proportion of the recording mark to thewhole of the one virtual recording cell varies with the irradiationamount of the recording laser beam. In short, in this multi-leveloptical recording medium, when the reproducing laser beam is irradiated,the light reflection ratio of the reproducing laser beam is affected bythe light transmission ratios of virtual recording cells formed withrecording marks, so that the reproducing laser beam is reflected atmultiple levels (e.g. five or more levels) of light reflection ratios.Therefore, by causing a plurality of data elements to be associated withmultiple levels of light reflection ratios, respectively, one virtualrecording cell stores one of the data elements. In this case, the term“light transmission ratio” is intended to mean a ratio of a laser beamhaving passed through the virtual recording cell to the reproducinglaser beam irradiated onto the virtual recording cell, and the term“light reflection ratio” is intended to mean a ratio of a laser beamwhich has passed through the virtual recording cell to be reflected by areflecting layer of the multi-level optical recording medium, and thenhas passed through the virtual recording cell again to be emitted out ofthe multi-level optical recording medium, to the reproducing laser beamirradiated onto the virtual recording cell.

In recording record data on the multi-level optical recording medium, itis necessary to perform recording such that individual data recorded atmultiple levels can be reliably identified when they are reproduced.Accordingly, it is preferable that there are certain degrees ofdifference between the respective light reflection ratios of virtualrecording cells having record data recorded thereon at multiple levels.On the other hand, materials used for the recording layer of themulti-level optical recording medium do not have respective uniquedegrees of change in properties with respect to the irradiation amountof the recording laser beam, but have different degrees of change inproperties depending on the characteristics thereof. Therefore, thelight reflection ratio of a virtual recording cell having a recordinglayer thereof unchanged in properties and the light reflection ratio ofa virtual recording cell having a recording layer thereof most changedin properties also vary with materials for the recording layer.Therefore, prior to recording record data, it is necessary to specify inadvance, for virtual recording cells in the multi-level opticalrecording medium, at least a light reflection ratio of virtual recordingcells having a recording layer thereof most changed in properties and alight reflection ratio of virtual recording cells having a recordinglayer thereof least changed in properties. To this end, in recordingrecord data on the multi-level optical recording medium at multiplelevels, the irradiation amount of the recording laser beam is switchedbetween the multiple levels, e.g. prior to recording the record data, tothereby vary the properties of virtual recording cells to the multiplelevels, and the respective light reflection ratios of the virtualrecording cells dependent on degrees of change in properties thereof aremeasured. This specifies the light reflection ratio of virtual recordingcells having a recording layer thereof most changed in properties andthe light reflection ratio of virtual recording cells having a recordinglayer thereof least changed in properties. Thereafter, the record datais recorded by controlling the light reflection ratio of a laser beam tomultiple levels according to the record data such that the respectivelight reflection ratios of virtual recording cells are included betweenthe two specified light reflection ratios.

On the other hand, in reproducing the record data recorded on themulti-level optical recording medium, it is possible to reproduce therecord data only by identifying which of the multiple levels of lightreflection ratios are exhibited by virtual recording cells having thereproducing laser beam irradiated thereon. Therefore, prior toreproducing the record data, it is necessary to identify in advance, inthe multi-level optical recording medium, at least the light reflectionratio of a virtual recording cell having the recording layer thereofmost changed in properties, and the light reflection ratio of a virtualrecording cell having the recording layer thereof least changed inproperties. Therefore, when record data recorded on the multi-leveloptical recording medium are reproduced, the respective light reflectionratios of a predetermined number of virtual recording cells are measuredsequentially from a first virtual recording cell, e.g. prior toreproduction of the record data, thereby identifying how many levels thelight reflection ratios of the virtual recording cells are defined intoand how the light reflection ratios of the virtual recording cells aredefined. After that, the record data are reproduced based on therespective identified levels of light reflection ratios.

DISCLOSURE OF THE INVENTION

From the study of the above described conventional multi-level opticalrecording medium, multi-level recording method, and multi-levelreproduction method, the present inventors found out the followingpoints for improvement: In the conventional multi-level recordingmethod, prior to recording record data, it is necessary to change theproperties of virtual recording cells to multiple levels and measure therespective light reflection ratios of the virtual recording cellsdependant on degrees of change in properties of the virtual recordingcells. Further, as described above, the materials used for the recordinglayer of the multi-level optical recording medium are different indegrees of change in properties with respect to the irradiation amountof the recording laser beam, depending on the characteristics of thematerials. On the other hand, when multi-level recording andreproduction is performed, it is preferable to use optimum ranges in thedynamic range of light reflection ratios (relative light reflectionratio dynamic range, which will be described in detail hereinafter)depending on the various kinds of materials for the recording layer. Forexample, a material A has a characteristic that a range of lightreflection ratios from a higher light reflection ratio of 95% to a lowerlight reflection ratio of 30% within the relative light reflection ratiodynamic range is suitable for multi-level recording and reproduction,whereas a material B has a characteristic that a range of lightreflection ratios from a higher light reflection ratio of 70% to a lowerlight reflection ratio of 10% within the relative light reflection ratiodynamic range is suitable for the same. Therefore, it is preferable touse an optimum range depending on the material. However, in theconventional multi-level recording and reproduction methods, it isdifficult to employ an optimum range within the above relative lightreflection ratio dynamic range, for the multi-level optical recordingmedium, which can undesirably decrease the reliability of themulti-level recording and reproduction. What is more, in theconventional multi-level reproduction method, it is necessary to measurerespective light reflection ratios of a predetermined number of virtualrecording cells prior to reproducing record data, and at the same timeidentify how many levels the light reflection ratios of virtualrecording cells are defined into and how the light reflection ratios ofvirtual recording cells are defined, based on the results of themeasurement. For this reason, although the recording and reproductionmethods are excellent, a process before the start of the recording orthe reproduction is troublesome, and it takes time to carry out theprocess. Furthermore, during recording, a precious data-recording areais consumed only to measure the respective light reflection ratiosdependent on degrees of change in properties of virtual recording cells.Therefore, it is preferable to improve these points.

The present invention has been made to solve the above describedproblems, and a main object thereof is to provide a multi-level opticalrecording medium, a multi-level recording method, and a multi-levelreproduction method, which are capable of carrying out multi-levelrecording and reproduction of record data promptly and easily with highreliability without wastefully using a data-recording area.

The multi-level optical recording medium according to the presentinvention is a multi-level optical recording medium capable of recordingrecord data according to multi-level recording that defines lightreflection ratios of recording portions into multiple levels byswitching an irradiation amount of a recording laser beam betweenmultiple levels, wherein light reflection ratio information enablingidentification of a light reflection ratio dynamic range within whichrespective light reflection ratios of the recording portions should beincluded is readably recorded.

According to this multi-level optical recording medium, the lightreflection ratio information enabling identification of the lightreflection ratio dynamic range within which the respective lightreflection ratios of the recording portions should be included isreadably recorded, whereby in recording record data, it is only requiredto record the record data such that the respective light reflectionratios of recording portions are included within the light reflectionratio dynamic range identified from the light reflection ratioinformation, and it is possible make it unnecessary to perform operationfor checking the characteristics of the multi-level optical recordingmedium prior to recording the record data. Therefore, it is possible torecord the record data promptly and easily with high reliability withoutwastefully using a data-recording area.

In this case, it is preferable that recording-portion light reflectionratio information enabling identification of a lowest light reflectionratio and a highest light reflection ratio out of the multiple levels oflight reflection ratios of the recording portions is recorded as thelight reflection ratio information. Due to this construction, it ispossible to uniquely define the lowest light reflection ratio and thehighest light reflection ratio based on the recording-portion lightreflection ratio information, and hence it is possible to record andreproduce recorded data promptly and easily.

Further, it is preferable that first light reflection ratio informationindicative of the lowest light reflection ratio, and second lightreflection ratio information indicative of the highest light reflectionratio are recorded as the recording-portion light reflection ratioinformation. Due to this construction, it is possible to immediatelyidentify values indicative of the lowest light reflection ratio and thehighest light reflection ratio, and hence it possible to record andreproduce record data more promptly and easily.

Furthermore, it is preferable that relative light reflection ratiosdefined by converting a value of a light reflection ratio of anunrecorded portion of the multi-level optical recording medium to 100%are recorded as the recording-portion light reflection ratioinformation. Due to this construction, in the multi-level opticalrecording medium in which the light reflection ratio of the unrecordedportion does not have a unique value but various values, the respectivelight reflection ratios of recording portions can be defined based onlight reflection ratios set with reference to the light reflection ratioof the unrecorded portion. This makes it possible to record andreproduce record data more promptly and easily in comparison with e.g. amulti-level optical recording medium on which absolute light reflectionratios defined by converting the value of a light reflection ratio of areference reflecting surface to 100% are recorded.

Further, it is preferable that the light reflection ratio information isrecorded in either of an area which is read out first by a recording andreproducing apparatus when the multi-level optical recording medium isloaded in the recording and reproducing apparatus, and an area which iscapable of being identified by area information recorded in the areawhich is read out first. Due to this construction, when record data isrecorded and reproduced, it is possible to cause the recording andreproducing apparatus to record and reproduce the record data reliablyand promptly since the light reflection ratio information is read outsimply by loading the multi-level optical recording medium in therecording and reproducing apparatus.

Further, it is preferable that the multi-level optical recording mediumis configured such that the record data can be recorded by multi-levelrecording at N levels (N is a natural number equal to or larger than 5),and recording data level information to the effect that the multi-leveloptical recording medium is a medium for recording the record data bythe multi-level recording at N levels is recorded. Due to thisconstruction, even if the number of levels to which light reflectionratios should be controlled is not fixed, it is possible to record andreproduce record data reliably and promptly according to the record datalevel information.

Further, it is preferable that the light reflection ratio information isrecorded by means of a wobble in a groove for guiding a reproducinglaser beam. Due to this construction, it is possible to prevent detailsof record data from being degraded due to the aging, thereby making itpossible to sufficiently enhance accuracy in reading the lightreflection ratio information.

The multi-level recording method according to the present invention is amulti-level recording method of recording record data by the multi-levelrecording on any of the multi-level optical recording media describedabove, wherein the light reflection ratio information is read out priorto recording the record data, and the record data is recorded such thatthe respective light reflection ratios of the recording portions areincluded within the light reflection ratio dynamic range identifiedbased on the light reflection ratio information read out.

According to this multi-level recording method, the light reflectionratio information is read out prior to recording record data, and therecord data is recorded such that the respective light reflection ratiosof recording portions are included within the light reflection ratiodynamic range identified based on the light reflection ratio informationread out, whereby it is possible to immediately record the record datawithout checking the characteristics of the multi-level opticalrecording medium prior to recording the record data, such that therespective light reflection ratios of the recording portions areincluded within the light reflection ratio dynamic range identified fromthe light reflection ratio information.

The multi-level reproduction method according to the present inventionis a multi-level reproduction method of reproducing record data recordedby the multi-level recording on any of the multi-level optical recordingmedia described above, wherein the recording-portion light reflectionratio information is read out prior to reproducing the record data, andrecord data which are read out at the lowest light reflection ratio andthe highest light reflection ratio identified based on therecording-portion light reflection ratio information, are reproduced asdata recorded with the smallest irradiation amount of the recordinglaser beam, and data recorded with the largest irradiation amount of therecording laser beam.

According to this multi-level reproduction method, recording-portionlight reflection ratio information is read out prior to reproduction ofrecord data, and record data read out at the lowest light reflectionratio and record data read out at the highest light reflection ratioidentified based on the recording-portion light reflection ratioinformation, are reproduced as data recorded with the smallestirradiation amount of the recording laser beam, and data recorded withthe largest irradiation amount of the recording laser beam,respectively, whereby it is possible to reliably and promptly reproducethe record data recorded on the multi-level optical recording medium atthe light reflection ratios, without checking the light reflectionratios prior to reproducing the record data, whenever the recorded dataare reproduced.

It should be noted that the present disclosure relates to the subjectmatter included in Japanese Patent Application No. 2001-169915 filed onJun. 5, 2001, and it is apparent that all the disclosures therein areincorporated herein by reference.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view, partly cut-away, to show the constructionof an optical recording medium 1 according to an embodiment of thepresent invention;

FIG. 2 is a conceptual view conceptually showing recording marks Ma toMg recorded in the optical recording medium 1;

FIG. 3 is a characteristics diagram showing the relative lightreflection ratio characteristics of optical recording media 1 formed byusing various kinds of organic dyes;

FIG. 4 is a characteristics diagram showing the relative lightreflection ratio characteristics of an organic dye used for a recordinglayer 12 of the optical recording medium 1; and

FIG. 5 is a block diagram showing the arrangement of an opticalrecording and reproducing apparatus 40.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, preferred embodiments of a multi-level optical recordingmedium, and a multi-level recording method and a multi-levelreproduction method for the multi-level optical recording medium,according to the present invention, will be described with reference tothe accompanying drawings.

First of all, the construction of the multi-level optical recordingmedium 1 (hereinafter also referred to as the “optical recording medium1”) according to the present invention will be described with referenceto FIG. 1.

The optical recording medium 1 is a CD-R optical recording medium(write-once/read-many type optical recording medium), and as shown inFIG. 1, is comprised of a substrate 11, a recording layer 12, areflecting film 13, and a protective layer 14. The substrate 11 isformed to have a disk shape, by using a transparent resin as a basematerial. In one surface (upper surface as viewed in FIG. 1) of thesubstrate 11 are spirally formed a groove 11 a for guiding a laser beam,and a land 11 b, from a location close to the central portion of thesubstrate 11 toward the outer periphery thereof. The recording layer 12is formed using an organic dye, such as cyanine, merocyanine, amethine-based dye and derivatives thereof, a benzenethiol metal complex,a phthalocyanine dye, a naphthalocyanine dye, or an azo dye, by applyingthe organic dye on the base 11 such that the organic dye covers thegroove 11 a and the land 11 b. The recording layer 12 is decomposed andchanged in properties by being irradiated with a laser beam by arecording apparatus, and the light transmission ratio of the recordinglayer 12 is changed according to the irradiation amount of the laserbeam. The reflecting film 13 is a thin film layer for reflecting areproducing laser beam having passed through the substrate 11 and therecording layer 12 when record data recorded on the optical recordingmedium 1 is reproduced, and is formed on the recording layer 12 e.g. bysputtering, using a metal, such as gold or silver, as a main rawmaterial. The protective layer 14 is for protecting the reflecting film13 and the recording layer 12, and formed in a manner covering the outersurface of the reflecting film 13.

Next, the recording principle of the optical recording medium 1 will bedescribed with reference to drawings.

Referring to FIG. 1, in the optical recording medium 1, virtualrecording cells S, S, . . . , which are obtained by virtually dividingthe groove 11 a along the direction of rotation (along thecircumference) of the optical recording medium 1, are defined as unitsfor recording. Now, as shown in FIG. 2, the length of each virtualrecording cell S in a direction along the groove 11 a is defined to besmaller than a focused beam diameter D (diameter of a beam waist).

In this case, the irradiation time of a recording laser beam (i.e. theirradiation amount of a laser beam) emitted from a pickup of therecording apparatus is controlled to multiple levels according to thevalues of recording data, whereby as shown in FIG. 2, recording marks Mato Mg (hereinafter, also referred to as the “recording marks M” whenthey are not discriminated from each other) which are different indegree of decomposition and change in properties of the recording layer12 (mainly made of an organic dye) are formed in the virtual recordingcells S. It should be noted that in the same figure, the degrees ofdecomposition and change in properties of the recording layer 12 areconceptually shown by the sizes of the recording marks M. Further, whenrecording data are recorded by the recording laser beam, the opticalrecording medium 1 is irradiated with the recording laser beam whilebeing rotated, which causes the recording marks M to have ellipticalshapes being lengths dependent on irradiation times.

Further, when multi-level recording is carried out on the opticalrecording medium 1, the respective degrees of decomposition and changein properties (the amounts of change in the light transmission ratio) ofthe recording marks Ma to Mg are defined such that the light reflectionratios of the virtual recording cells S exhibited when the reproducinglaser beam is irradiated onto the virtual recording cells S are e.g. atseven levels (eight levels when an unrecorded portion is included). Inthis case, each light reflection ratio is larger as the degree ofdecomposition and change in properties of the recording layer 12 issmaller. Therefore, a virtual recording cell S with no recording markrecorded thereon has the characteristic of a maximum light reflectionratio, and the virtual recording cell S with the smallest recording markMa recorded thereon has the characteristic of the largest lightreflection ratio of all the virtual recording cells S with the recordingmarks M recorded thereon. The respective virtual recording cells Shaving the recording marks Mb to Mf recorded thereon are reduced inlight reflection ratio in the order of the recording marks Mb to Mf, andthe virtual recording cell S with the largest recording mark Mg recordedthereon has the characteristic of the minimum light reflection ratio.Therefore, by properly setting the area ratios of portions decomposedand changed in properties (i.e. the light transmission ratios of therecording layer 12) by controlling the irradiation amount of the laser,it is possible to form the recording marks Ma to Mg having respectiveseven levels of light reflection ratios.

Next, the characteristics of the organic dyes used for forming therecording layer 12 of the optical recording medium 1 will be describedwith reference to drawings.

In general, organic dyes used for the recording layer 12 have acharacteristic that as the irradiation time (irradiation amount) of therecording laser beam is increased, the degree of decomposition andchange in properties of each organic dye is also increased. On the otherhand, the change in light reflection ratio in this case is not linearwith respect to the irradiation time (irradiation amount) of therecording laser beam. Further, the degree of decomposition and change inproperties of the organic dye, dependent on the irradiation time(irradiation amount) of the recording laser beam, has a characteristicthat the degree is gently increased for some time from the start of theirradiation, and sharply and linearly increased after the lapse of apredetermined time period. Then, it is gently increased again, and afterthe irradiation time has exceeded a certain time period, it is hardlyincreased. Further, the light transmission ratio of the organic dyewhich is not decomposed or changed in properties, the light transmissionratio of the organic dye which is most decomposed and changed inproperties (the organic dye which has been decomposed and changed inproperties to such an extent that the degree of decomposition and changein properties thereof is hardly increased), and the amount of change inthe light transmission ratio corresponding to a degree of decompositionand change in properties of the organic dye also vary with the materialof an organic dye used. Therefore, assuming that e.g. five kinds ofoptical recording media 1 are produced which have recording layers 12formed by organic dyes different from each other, respective absolutelight reflection ratios of the recording layers 12 of the opticalrecording media 1 are different from each other. In this case, the term“absolute light reflection ratio” is intended to mean a light reflectionratio of an unrecorded portion (unrecorded virtual recording cell S) ofthe recording layer 12 of each optical recording medium 1, which ismeasured in comparison with a reference light reflection ratio, assumingthat the value of a light reflection ratio of a disk body having a thinfilm of gold or the like formed on a smooth surface thereof e.g. bysputtering, is converted to the reference light reflection ratio (100%).Further, the characteristics of relative light reflection ratios on therecording layers 12 of the optical recording media 1 are also differentfrom each other, as shown by characteristic curves C1 to C5 appearing inFIG. 3. It should be noted that as shown in the same figure, theaforementioned degree of the decomposition and change in properties ofthe organic dye contributes to the inclination of each of thecharacteristic curves C1 to CS. In this case, the term “relative lightreflection ratio” is intended to mean a ratio of the light reflectionratio dependent on an irradiation time of a recording portion (i.e. arecorded virtual recording cell S) of the recording layer 12 of eachoptical recording medium 1, provided that the value of the absolutelight reflection ratio of an unrecorded portion (i.e. an unrecordedvirtual recording cell S) of the recording layer 12 of each opticalrecording medium 1 is converted to 100%. Further, the absolute lightreflection ratios and the relative light reflection ratios are differenton an organic dye-by-organic dye basis, which causes characteristics,such as modulations, dynamic ranges, jitter characteristics, and B.E.R(Bit Error Rate), of the optical recording media 1 to be also differentfrom each other. Furthermore, the above characteristics also vary notonly with the material of an organic dye but also with parameters, suchas thickness of coating of the organic dye, the structure of the groove11 a (the depth, width, and shape thereof), and the material of areflecting film 13.

In this case, since the multi-level recording cannot be carried out onthe optical recording medium 1, until the light reflection ratio of theoptical recording medium 1 is accurately controlled to multiple levels,it is difficult to reproduce record data recorded at multiple levelsunless the absolute light reflection ratio of a recording portion(unrecorded virtual recording cell S) having the largest lightreflection ratio is large to some extent (e.g. 40% to 80%), and at thesame time the difference in light reflection ratio between a recordingportion having the largest absolute light reflection ratio, and arecording portion (virtual recording cell S formed with the recordingmark Mg) having the smallest absolute light reflection ratio is large tosome extent. As the absolute light reflection ratio is larger, it ismore preferable. However, in general, it is difficult to secure a valuelarger than 80%, since the amount of the reproducing laser beam returnedto the pickup of a playback apparatus is reduced due to diffusereflection caused depending on the above characteristics of theparameters and the structure of the groove 11 a. Further, when a valueof the light reflection ratio of a recording portion (unrecorded virtualrecording cell S), which is not decomposed or changed in properties, isconverted to 100% and a ratio of a value of the light reflection ratioof a recording portion most decomposed and changed in properties(virtual recording cell S decomposed and changed in properties to suchan extent that the degree of decomposition and change in properties ishardly increased) is defined as a relative light reflection ratiodynamic range, the relative light reflection ratio is nonlinearlychanged with respect to the irradiation time (irradiation amount) of thelaser beam due to the characteristics of the organic dye describedabove, in an unrecorded portion-side region (approximately two tenths)of the relative light reflection ratio dynamic range, and a region(approximately two tenths) of the relative light reflection ratiodynamic range on the side of the recording portion most decomposed andchanged in properties, whereas in a region of approximately six tenthsof the relative light reflection ratio dynamic range, as an intermediateregion between the aforementioned two regions, the relative lightreflection ratio is linearly changed with respect to the irradiationtime. Therefore, it is preferable that in the optical recording medium1, the absolute light reflection ratio of a recording portion having thelargest light reflection ratio is within a range of 40% to 80%, and thedifference in light reflection ratio between a recording portion havingthe largest absolute light reflection ratio (virtual recording cell Sformed with the recording mark Ma) and a recording portion having thesmallest absolute light reflection ratio (virtual recording cell Sformed with the recording mark Mg) is larger than 40 points. It shouldbe noted that the ratio between the above two regions each occupyingapproximately two tenths of the range on the unrecorded portion side andthe recording portion side, and the region occupying approximately sixtenths of the same as the intermediate region between the above tworegions largely depends on the characteristics of an organic dye usedfor the recording layer 12, and cannot be defined unconditionally.

Next, the characteristics of the optical recording medium 1 will bedescribed in further detail with reference to FIG. 4. It should be notedthat the following description will be given assuming that the recordinglayer 12 of the optical recording medium 1 is formed by using an organicdye having characteristics indicated by the characteristic curve C1shown in FIG. 3.

In the recording layer 12 of the above optical recording medium 1, whenthe value of the light reflection ratio (light reflection ratioindicated by a point P0 on the characteristic curve C1) of part thereofwhich is not decomposed or changed in properties, is converted to 100%,in a relative light reflection ratio dynamic range Ra1 set by the aboveconversion, the light reflection ratio (light reflection ratio indicatedby a point P1 on the characteristic curve C1) of a portion mostdecomposed and changed in properties is e.g. 10%. Therefore, therelative light reflection ratios of the virtual recording cells S havingthe recording marks Ma to Mg recorded thereon, respectively, are definedsuch that they are included in the region occupying approximately sixtenths of the relative light reflection ratio dynamic range Ra1 as theintermediate region. In this case, it is preferable that differences(intervals) between the respective relative light reflection ratios(light reflection ratios indicated by points Pa to Pg on thecharacteristic curve C1) of the virtual recording cells S having therecording marks Ma to Mg recorded thereon are approximately even.Therefore, the relative light reflection ratios are defined to be e.g.82%, 73%, 64%, 55%, 46%, 37%, and 28%, respectively. Hereinafter, theregion including the respective relative light reflection ratios of thevirtual recording cells S, S, . . . having the respective recordingmarks Ma to Mg recorded thereon is also referred to as the “recordingportion relative light reflection ratio dynamic range Rav”. It should benoted that the values of the aforementioned relative light reflectionratios largely depend on the characteristics of an organic dye used forthe recording layer 12, and cannot be defined unconditionally.

In the above case, the values defined as the respective relative lightreflection ratios of the virtual recording cells S having the recordingmarks Ma to Mg recorded thereon are different from each other dependinge.g. on the material of an organic dye used for the recording layer 12,as described above. Therefore, in the optical recording medium 1,information enabling identification of the recording portion relativelight reflection ratio dynamic range Rav dependent on the material of anorganic dye used for the recording layer 12 and the like is recorded inadvance when the optical recording medium 1 is produced, whereby valuesto be defined as the respective relative light reflection ratios of thevirtual recording cells S having the recording marks Ma to Mg recordedthereon are defined. More specifically, in the optical recording medium1, light reflection ratio information (first light reflection ratioinformation in the present invention; hereinafter also referred to asthe “maximum light reflection ratio information”) concerning a maximumlight reflection ratio in the recording portion relative lightreflection ratio dynamic range Rav, and light reflection ratioinformation (second light reflection ratio information in the presentinvention; hereinafter also referred to as the “minimum light reflectionratio information”) concerning a minimum light reflection ratio in therecording portion relative light reflection ratio dynamic range Rav arerecorded in a lead-in area e.g. by means of a wobble. In this case, thelead-in area is an area which is read out first when the opticalrecording medium 1 is loaded in a recording and reproducing apparatus.In the optical recording medium 1, there are recorded not only themaximum light reflection ratio information and the minimum lightreflection ratio information but also various kinds of information, suchas information to the effect that the optical recording medium 1 is amulti-level optical recording medium (hereinafter also referred to asthe “medium identifying information”), and information to the effectthat data is recorded by the multi-level recording at seven levelsexclusive of an unrecorded portion having no recording mark M recordedthereon (hereinafter also referred to as the “recording data levelinformation”). Further, the wobble is fixedly formed as a very slightmeandering portion of the groove 11 a when the substrate 11 is molded.Therefore, it is possible to prevent the recorded data from beingdegraded due to the aging, thereby making it possible to enhanceaccuracy in the reading of the light reflection ratio information.

Next, an optical recording and reproducing apparatus 40 for recordingrecord data on the optical recording medium 1, and reproducing therecorded data will be described with reference to FIG. 5.

The optical recording and reproducing apparatus 40 is a so-called CD-Rrecorder, and includes a spindle servo 41, a spindle motor 42, a pickup43, a focus tracking servo 44, a feed servo 55, and a control system 46.In the present embodiment, the spindle motor 42 is driven by the spindleservo 41 to rotate the optical recording medium 1 at a constant linearvelocity. In the pickup 43, a laser, not shown, is driven by a laserdriver, not shown, under the control of the control system 46, tothereby irradiate a recording laser beam or a reproducing laser beam tothe optical recording medium 1. As a result, the recording marks M arerecorded on virtual recording cells S, and an electric signal is outputaccording to the levels of laser beams reflected from the virtualrecording cells S having the recording marks M recorded thereon. In thiscase, when the record data is recorded, the laser driver of the pickup43 adjusts the irradiation amount (the number of laser pulses, and/orirradiation power, pulse height, etc.) of the laser beam irradiated ontoone virtual recording cell S, in accordance with control of the controlsystem 46, depending on details of record data. It should be noted thatthe irradiation amount of a laser beam can be adjusted not only by theadjusting method using the laser driver but also by a method ofcontrolling the driving of an optical modulator disposed on an opticalpath of the laser beam by the control system 46.

Further, the pickup 43 includes an objective lens and a half mirror,neither of which is shown, to thereby cause a recording or reproducinglaser beam to be focuses onto the recording layer 12 of the opticalrecording medium 1. More specifically, the objective lens is controlledby the focus tracking servo 44, whereby the recording or reproducinglaser beam is focused onto the recording layer 12 of the opticalrecording medium 1. The pickup 43 is caused to reciprocate by the feedservo 45 along the direction of the diameter of the optical recordingmedium 1 between the inner periphery side and the outer periphery sideof the optical recording medium 1. The control system 46 controlsdriving of the spindle servo 41, the pickup 43, the focus tracking servo44, and the feed servo 45, and reads record data recorded on therecording layer 12 based on the electric signal output from the pickup.

Next, a description will be given of the multi-level recording method ofrecording record data on the optical recording medium 1 by the opticalrecording and reproducing apparatus 40.

First, when the optical recording medium 1 is loaded in the opticalrecording and reproducing apparatus 40, the control system 46 controlsthe spindle servo 41 to thereby drive the spindle motor 42 for rotationof the optical recording medium 1. At the same time, the control system46 drives the feed servo 45 to move the pickup 43 to the lead-in area.Then, the control system 46 causes the pickup 43 to emit the readinglaser beam, and at the same time drives the focus tracking servo 44 forfocus and tracking control of the objective lens of the pickup 43. As aresult, the laser beam emitted from the pickup 43 is irradiated onto thelead-in area of the optical recording medium 1, and the reflected laserbeam from the lead-in area is received by the pickup 43. In this step,the electric signal is output from the pickup 43 according to variouskinds of information, such as the medium identifying information, themaximum light reflection ratio information, the minimum light reflectionratio information, and the record data level information, which arerecorded in the lead-in area e.g. by means of a wobble, and based on theelectric signal, the control system 46 reads the various kinds ofinformation.

In this step, the control system 46 determines based on the read mediumidentifying information that the optical recording medium 1 is amulti-level optical recording medium. Next, the control system 46identifies the recording portion relative light reflection ratio dynamicrange Rav of the optical recording medium 1, based on the maximum lightreflection ratio information and the minimum light reflection ratioinformation. Then, the control system 46 defines the respective relativelight reflection ratios of the virtual recording cells S having theseven levels of recording marks Ma to Mg recorded thereon, as 82%, 73%,64%, 55%, 46%, 37%, and 28%, based on the identified recording portionrelative light reflection ratio dynamic range Rav and the record datalevel information. After that, when record data is recorded, the controlsystem 46 records the recording marks Ma to Mg corresponding to thedetails of the data such that the recording marks Ma have the definedrelative light reflection ratios, respectively. More specifically, thecontrol system 46 controls the laser driver of the pickup 43 accordingto the recording marks M to be recorded, whereby the laser drivercontrols the irradiation amount of the recording laser beam irradiatedonto one virtual recording cell S. Thus, the recording marks Ma to Mgcorresponding to the details of the record data are sequentiallyrecorded on the virtual recording cells S, S, . . . .

Next, a description will be given of the reproduction method ofreproducing record data recorded on the optical recording medium 1 bythe optical recording and reproducing apparatus 40.

First, as described above, when the optical recording medium 1 is loadedin the optical recording and reproducing apparatus 40, the controlsystem 46 reads various kinds of information, such as the mediumidentifying information, the maximum light reflection ratio information,the minimum light reflection ratio information, and the record datalevel information, which are recorded in the lead-in area. Next, thecontrol system 46 determines based on the read medium identifyinginformation that the optical recording medium 1 is a multi-level opticalrecording medium, and identifies the recording portion relative lightreflection ratio dynamic range Rav of the optical recording medium 1,based on the maximum light reflection ratio information and the minimumlight reflection ratio information. Then, the control system 46 definesthe respective relative light reflection ratios of the virtual recordingcells S having the seven levels of recording marks Ma to Mg recordedthereon, as 82%, 73%, 64%, 55%, 46%, 37%, and 28%, based on theidentified recording portion relative light reflection ratio dynamicrange Rav and the record data level information. After that, the controlsystem 46 reads the record data, assuming that the respective recordingmarks Ma to Mg are recorded on the virtual recording cells S havingrelative light reflection ratios of 82%, 73%, 64%, 55%, 46%, 37%, and28%, respectively. Thus, the record data recorded on the opticalrecording medium 1 are reproduced. Although for ease of understandingthe present invention, the description has been given using the valuesof the relative light reflection ratios given by way of example, this isnot limitative. More specifically, the size of the virtual recordingcell S, and the diameter of the focused recording or reproducing beam isselected as required. Therefore, the optical recording and reproducingapparatus 40 reads out record data after defining the relative lightreflection ratios of the virtual recording cells S as required inaccordance with a combination of the size of the virtual recording cellsS and the diameter of the focused beam, such that influence of adjacentvirtual recording cells S on the relative light reflection ratiosfunctioning as thresholds can be eliminated as much as possible inreproducing the record data.

As described hereinabove, according to the optical recording medium 1,the maximum light reflection ratio information and the minimum lightreflection ratio information, which enable identification of therecording portion relative light reflection ratio dynamic range Ravwhich should be defined as the relative light reflection ratios of thevirtual recording cells S having the recording marks Ma to Mg recordedthereon, respectively, are recorded in advance when the opticalrecording medium 1 is produced, whereby it is made possible toimmediately identify relative light reflection ratios which should bedefined as the relative light reflection ratios of the virtual recordingcells S having the recording marks Ma to Mg recorded thereon, withoutcarrying out a measurement process in which the virtual recording cellsS are changed in properties to multiple levels to thereby measure lightreflection ratios respectively dependent on degrees of change inproperties of the virtual recording cells S, or a measurement processfor measuring respective light reflection ratios of a predeterminednumber of virtual recording cells S, S, . . . . Therefore, when recorddata is recorded on the optical recording medium 1, it is possible todefine the respective relative light reflection ratios of the virtualrecording cells S having the recording marks Ma to Mg recorded thereon,based on the recording portion relative light reflection ratio dynamicrange Rav which is identified from the two pieces of the lightreflection ratio information, and reliably record the recording marks Mato Mg such that the recording marks Ma to Mg have the defined relativelight reflection ratios, respectively. As a result, the record data canbe recorded promptly and easily. Moreover, light reflection ratioinformation defining an optimum range of the relative light reflectionratio dynamic range, dependent on the material of the recording layer 12is recorded in advance, whereby it is possible to sufficiently increasethe reliability of the multi-level recording and reproduction. Further,when record data recorded on the optical recording medium 1 isreproduced, it is possible to define the respective relative lightreflection ratios of the virtual recording cells S having the recordingmarks Ma to Mg recorded thereon, based on the identified recordingportion relative light reflection ratio dynamic range Rav, andimmediately read the recording marks Ma to Mg based on the definedrelative light reflection ratios. As a result, the record data can bereproduced promptly and easily.

Further, according to the optical recording medium 1, the maximum lightreflection ratio information and the minimum light reflection ratioinformation are recorded in the lead-in area, whereby when the opticalrecording medium 1 is loaded in the optical recording and reproducingapparatus, the maximum light reflection ratio information and theminimum light reflection ratio information are read in by the opticalrecording and reproducing apparatus prior to recording or reproducingrecord data, and hence it is possible to cause the optical recording andreproducing apparatus to record the recording marks M in a mannercorresponding to the recording portion relative light reflection ratiodynamic range Rav dependent on the characteristics of the recordinglayer 12 and to accurately read the recording marks M recorded thereon.

It should be noted that the present invention is not limited to theabove embodiment, but it can be modified as required. For example,although in the above described embodiment, an organic dye is employedfor the recording layer 12 by way of example, this is not limitative,but the multi-level optical recording medium according to the presentinvention can also be applied to a multi-level optical recording mediumusing an organic dye other than the above-mentioned organic dyes or aninorganic material, for the recording layer 12. It can also be appliedto a multi-level optical recording medium for multi-level recording byphase transition or magneto-optics. Further, although in the abovedescribed embodiment, the optical recording medium 1 is formed as a CD-Roptical recording medium by way of example, this is not limitative, butthe present invention can be generally applied to other recording media.Furthermore, the present invention is not limited to a disk-shapedrotary body. Further, although in the above described embodiment, theoptical recording medium 1 is configured such that recording andreproducing laser beams are irradiated from the substrate 11 side, theoptical recording medium 1 can also be applied to an optical recordingmedium configured such that a reflecting layer, a recording layer, and aprotective layer are sequentially deposited on a substrate and therecording and reproducing laser beams are irradiated from the protectivelayer side. Further, the values of the light reflection ratios shown inthe above described embodiment are given by way of example for ease ofunderstanding the present invention, and hence can be changed asrequired. Furthermore, the multi-level optical recording mediumaccording to the present invention includes various kinds of multi-leveloptical recording media on which multi-level recording can be carriedout at a plurality of levels so long as the multi-level recording can becarried out at five levels or more.

Further, although in the above described embodiment, the maximum lightreflection ratio information and the minimum light reflection ratioinformation as first reflectance information and second light reflectionratio information in the present invention are recorded by way ofexample, this is not limitative, but light reflection ratio informationin the present invention may be, for example, information to the effectthat a predetermined light reflection ratio is set to a reference lightreflection ratio, and light reflection ratios in a range of several %larger than the light reflection ratio to several % smaller than thesame are used, or information enabling identification of a lightreflection ratio dynamic range within which the respective lightreflection ratios of recording portions having the recording marks Mrecorded thereon should be included. In this case, the informationenabling identification of the light reflection ratio dynamic rangewithin which the respective light reflection ratios of the recordingportions should be included is intended to mean information to theeffect that the recording marks M be recorded such that the respectivelight reflection ratios of the recording portions are included within arange of a relative light reflection ratio of 85% to a relative lightreflection ratio of 15%. Therefore, when the recording marks Ma to Mgare recorded based on the information, they may be recorded e.g. bysetting the relative light reflection ratio of a virtual recording cellS having the recording mark Ma recorded thereon to 70%, and the relativelight reflection ratio of a virtual recording cell S having therecording mark Mg recorded thereon to 30%.

Further, although in the embodiment of the present invention, themaximum light reflection ratio information and the minimum lightreflection ratio information are recorded as relative light reflectionratios defined by converting a value of the light reflection ratio of anunrecorded portion having no recording mark M recorded thereon to 100%by way of example, this is not limitative, but it is also possible torecord, as light reflection ratio information, absolute light reflectionratios defined by converting a value of the light reflection ratio of adisk body having a thin film of gold or the like formed on a smoothsurface thereof e.g. by sputtering, to a reference light reflectionratio (100%). Further, although in the embodiment of the presentinvention, light reflection ratio information in the present inventionis recorded in the lead-in area by means of a wobble by way of example,this is not limitative, but the light reflection ratio information maybe recorded in any recording area so long as it is a recording areacapable of being identified based on information recorded in the lead-inarea, and the method of recording the light reflection ratio informationis not limited to that using a wobble. For example, the light reflectionratio information can also be recorded by the groove 11 a or a prepit ofthe land 11 b, or recorded on the recording layer 12 by a recordinglaser beam. What is more, although the embodiment of the presentinvention is described taking the example of recording, in advance,information (recording data level information) to the effect thatrecording is carried out by multi-level recording at eight levelsinclusive of that of an unrecorded portion, when the optical recordingmedium 1 is produced, the record data level information in the presentinvention is not always necessary. For example, when the number oflevels of record data is defined in advance in a standard concerning themulti-level recording method, the record data-level information need notbe recorded, but it is only required to control the light reflectionratios to multiple levels according to the standard.

INDUSTRIAL APPLICABILITY

As described hereinbefore, according to the multi-level opticalrecording medium of the present invention, light reflection ratioinformation enabling identification of a light reflection ratio dynamicrange within which the respective light reflection ratios of recordingportions should be included is readably recorded, whereby in recodingrecord data, it is only required to record the record data such that therespective light reflection ratios of recording portions are includedwithin the light reflection ratio dynamic range identified from thelight reflection ratio information. This can make it unnecessary tocheck the characteristics of the multi-level optical recording mediumprior to recording the record data, so that it is possible to record therecord data promptly and easily with high reliability without wastefullyusing a data-recording area. This makes it possible to realize amulti-level optical recording medium on which multi-level recording andreproduction of record data can be carried out promptly and easily withhigh reliability without wastefully using a data-recording area.

Further, according to the multi-level recording method of the presentinvention, the light reflection ratio information is read out beforerecord data is recorded, and the record data is recorded such that therespective light reflection ratios of recording portions are includedwithin the light reflection ratio dynamic range identified based on thelight reflection ratio information read out, whereby it is possible toimmediately record the record data without checking the characteristicsof the multi-level optical recording medium prior to recording therecord data, such that the respective light reflection ratios of therecording portions are included within the light reflection ratiodynamic range identified from the light reflection ratio information.This makes it possible to realize a multi-level recording method onwhich multi-level recording of record data can be performed promptly andeasily with high reliability without wastefully using a data-recordingarea.

Further, according to the multi-level reproduction method of the presentinvention, recording-portion light reflection ratio information is readout prior to reproduction of record data, and the record data which areread out at the lowest light reflection ratio and the highest lightreflection ratio identified based on the recording-portion lightreflection ratio information, are reproduced as record data recordedwith the smallest irradiation amount of a recording laser beam, andrecord data recorded with the largest irradiation amount of therecording laser beam, whereby it is possible to reliably and promptlyreproduce the record data recorded on the multi-level optical recordingmedium at the light reflection ratios, without checking the lightreflection ratios prior to reproducing the record data whenever therecord data is reproduced. This makes it possible to realize amulti-level reproduction method which is capable of carrying outmulti-level reproduction of record data promptly and easily with highreliability without wastefully using a data-recording area.

1. A multi-level optical recording medium capable of recording recorddata according to a multi-level recording that defines light reflectionratios of recording portions into multiple levels by switching anirradiation amount of a recording laser beam between multiple levels,wherein light reflection ratio information enabling identification of alight reflection ratio dynamic range within which respective lightreflection ratios of the recording portions should be included isreadably recorded, wherein recording-portion light reflection ratioinformation enabling identification of a lowest light reflection ratioand a highest light reflection ratio out of the multiple levels of lightreflection ratios of the recording portions is recorded as the lightreflection ratio information.
 2. A multi-level optical recording mediumas claimed in claim 1, wherein first light reflection ratio informationindicative of the lowest light reflection ratio, and second lightreflection ratio information indicative of the highest light reflectionratio are recorded as the recording-portion light reflection ratioinformation.
 3. A multi-level optical recording medium as claimed inclaim 2, wherein relative light reflection ratios defined by convertinga value of a light reflection ratio of an unrecorded portion of themulti-level optical recording medium to 100% are recorded as therecording-portion light reflection ratio information.
 4. A multi-leveloptical recording medium as claimed in claim 2, wherein the lightreflection ratio information is recorded in either of an area which isread out first by a recording and reproducing apparatus when themulti-level optical recording medium is loaded in the recording andreproducing apparatus, and an area which is capable of being identifiedby area information recorded in the area which is read out first.
 5. Amulti-level optical recording medium as claimed in claim 2, which isconfigured such that the record data can be recorded by multi-levelrecording at N levels (N is a natural number at least equal to 5), andwherein recording data level information to the effect that themulti-level optical recording medium is a medium for recording therecord data by the multi-level recording at N levels is recordedthereon.
 6. A multi-level optical recording medium as claimed in claim2, wherein the light reflection ratio information is recorded by meansof a wobble in a groove for guiding a reproducing laser beam.
 7. Amulti-level optical recording medium as claimed in claim 1, whereinrelative light reflection ratios defined by converting a value of alight reflection ratio of an unrecorded portion of the multi-leveloptical recording medium to 100% are recorded as the recording-portionlight reflection ratio information.
 8. A multi-level optical recordingmedium as claimed in claim 7, wherein the light reflection ratioinformation is recorded in either of an area which is read out first bya recording and reproducing apparatus when the multi-level opticalrecording medium is loaded in the recording and reproducing apparatus,and an area which is capable of being identified by area informationrecorded in the area which is read out first.
 9. A multi-level opticalrecording medium as claimed in claim 7, which is configured such thatthe record data can be recorded by multi-level recording at N levels (Nis a natural number at least equal to 5), and wherein recording datalevel information to the effect that the multi-level optical recordingmedium is a medium for recording the record data by the multi-levelrecording at N levels is recorded thereon.
 10. A multi-level opticalrecording medium as claimed in claim 7, wherein the light reflectionratio information is recorded by means of a wobble in a groove forguiding a reproducing laser beam.
 11. A multi-level optical recordingmedium as claimed in claim 1, wherein the light reflection ratioinformation is recorded in either of an area which is read out first bya recording and reproducing apparatus when the multi-level opticalrecording medium is loaded in the recording and reproducing apparatus,and an area which is capable of being identified by area informationrecorded in the area which is read out first.
 12. A multi-level opticalrecording medium as claimed in claim 1, which is configured such thatthe record data can be recorded by multi-level recording at N levels (Nis a natural number at least equal to 5), and wherein recording datalevel information to the effect that the multi-level optical recordingmedium is a medium for recording the record data by the multi-levelrecording at N levels is recorded thereon.
 13. A multi-level opticalrecording medium as claimed in claim 1, wherein the light reflectionratio information is recorded by means of a wobble in a groove forguiding a reproducing laser beam.
 14. A multi-level recording method ofrecording record data by the multi-level recording on the multi-leveloptical recording medium as claimed in claim 1, wherein the lightreflection ratio information is read out prior to recording the recorddata, and the record data is recorded such that the respective lightreflection ratios of the recording portions are included within thelight reflection ratio dynamic range identified based on the lightreflection ratio information read out.
 15. A multi-level reproductionmethod of reproducing record data recorded by the multi-level recordingon the multi-level optical recording medium as claimed in claim 1,wherein the recording-portion light reflection ratio information is readout prior to reproducing the record data, and record data which are readout at the lowest light reflection ratio and the highest lightreflection ratio identified based on the recording-portion lightreflection ratio information, are reproduced as data recorded with thesmallest irradiation amount of the recording laser beam, and datarecorded with the largest irradiation amount of the recording laserbeam.